1. Field of the Invention
This invention relates to a device for turning the nuts and/or tensioning nuts of several studs arranged on a pitch circle for closing a pressure vessel, especially a reactor pressure vessel. More particularly, the invention relates to tensioning assemblies having separate or unitary support bodies which provide space for receiving such nuts together with studs and, if applicable, tensioning bolts, and to which separate turning units and, more particularly, reversible electric motors, are fastened. Each such turning unit drives a pinion meshing with teeth on a drive bushing which is supported in the support body, surrounds the stud or tensioning bolt and transmits the torque to the nut.
2. Discussion of the Prior Art
A tensioner of this kind is described in German Patent No. 22 58 859 and corresponding U.S. Pat. No. 3,877,326. There a tightening nut being screwed onto a stud is set in rotation by the pinion of a turning unit in such a way that the latter meshes with the external teeth of a drive bushing. Internal teeth in the drive bushing engage external teeth on the nut. The drive bushing is supported axially and radially in the support body of the device. The presence of such external teeth on the nut weakens its cross-sectional strength. In addition, the drive bushing is difficult to manufacture due to the internal and external teeth.
It is, therefore, an object of the invention to make possible the transmission of torque to the entire circumference of a nut or tensioning nut without the use of external gearing on the nut.